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<b>Figures xv</b> <p><b>Tables xix</b></p> <p><b>Equations xxi</b></p> <p><b>Preface and Acknowledgments xxiii</b></p> <p>Audience xxiv</p> <p>Organization xxiv</p> <p>Acknowledgments xxvi</p> <p><b>PART 1 BASICS 1</b></p> <p><b>1 SERVICE, RISK, AND BUSINESS CONTINUITY 3</b></p> <p>1.1 Service Criticality and Availability Expectations 3</p> <p>1.2 The Eight-Ingredient Model 4</p> <p>1.3 Catastrophic Failures and Geographic Redundancy 7</p> <p>1.4 Geographically Separated Recovery Site 11</p> <p>1.5 Managing Risk 12</p> <p>1.6 Business Continuity Planning 14</p> <p>1.7 Disaster Recovery Planning 15</p> <p>1.8 Human Factors 17</p> <p>1.9 Recovery Objectives 17</p> <p>1.10 Disaster Recovery Strategies 18</p> <p><b>2 SERVICE AVAILABILITY AND SERVICE RELIABILITY 20</b></p> <p>2.1 Availability and Reliability 20</p> <p>2.2 Measuring Service Availability 25</p> <p>2.3 Measuring Service Reliability 33</p> <p><b>PART 2 MODELING AND ANALYSIS OF REDUNDANCY 35</b></p> <p><b>3 UNDERSTANDING REDUNDANCY 37</b></p> <p>3.1 Types of Redundancy 37</p> <p>3.2 Modeling Availability of Internal Redundancy 44</p> <p>3.3 Evaluating High-Availability Mechanisms 52</p> <p><b>4 OVERVIEW OF EXTERNAL REDUNDANCY 59</b></p> <p>4.1 Generic External Redundancy Model 59</p> <p>4.2 Technical Distinctions between Georedundancy and Co-Located Redundancy 74</p> <p>4.3 Manual Graceful Switchover and Switchback 75</p> <p><b>5 EXTERNAL REDUNDANCY STRATEGY OPTIONS 77</b></p> <p>5.1 Redundancy Strategies 77</p> <p>5.2 Data Recovery Strategies 79</p> <p>5.3 External Recovery Strategies 80</p> <p>5.4 Manually Controlled Recovery 81</p> <p>5.5 System-Driven Recovery 83</p> <p>5.6 Client-Initiated Recovery 85</p> <p><b>6 MODELING SERVICE AVAILABILITY WITH EXTERNAL SYSTEM REDUNDANCY 98</b></p> <p>6.1 The Simplistic Answer 98</p> <p>6.2 Framing Service Availability of Standalone Systems 99</p> <p>6.3 Generic Markov Availability Model of Georedundant Recovery 103</p> <p>6.4 Solving the Generic Georedundancy Model 115</p> <p>6.5 Practical Modeling of Georedundancy 121</p> <p>6.6 Estimating Availability Benefit for Planned Activities 130</p> <p>6.7 Estimating Availability Benefit for Disasters 131</p> <p><b>7 UNDERSTANDING RECOVERY TIMING PARAMETERS 133</b></p> <p>7.1 Detecting Implicit Failures 134</p> <p>7.2 Understanding and Optimizing RTO 141</p> <p><b>8 CASE STUDY OF CLIENT-INITIATED RECOVERY 147</b></p> <p>8.1 Overview of DNS 147</p> <p>8.2 Mapping DNS onto Practical Client-Initiated Recovery Model 148</p> <p>8.3 Estimating Input Parameters 154</p> <p>8.4 Predicted Results 165</p> <p>8.5 Discussion of Predicted Results 172</p> <p><b>9 SOLUTION AND CLUSTER RECOVERY 174</b></p> <p>9.1 Understanding Solutions 174</p> <p>9.2 Estimating Solution Availability 177</p> <p>9.3 Cluster versus Element Recovery 179</p> <p>9.4 Element Failure and Cluster Recovery Case Study 182</p> <p>9.5 Comparing Element and Cluster Recovery 186</p> <p>9.6 Modeling Cluster Recovery 187</p> <p><b>PART 3 RECOMMENDATIONS 201</b></p> <p><b>10 GEOREDUNDANCY STRATEGY 203</b></p> <p>10.1 Why Support Multiple Sites? 203</p> <p>10.2 Recovery Realms 204</p> <p>10.3 Recovery Strategies 206</p> <p>10.4 Limp-Along Architectures 207</p> <p>10.5 Site Redundancy Options 208</p> <p>10.6 Virtualization, Cloud Computing, and Standby Sites 216</p> <p>10.7 Recommended Design Methodology 217</p> <p><b>11 MAXIMIZING SERVICE AVAILABILITY VIA GEOREDUNDANCY 219</b></p> <p>11.1 Theoretically Optimal External Redundancy 219</p> <p>11.2 Practically Optimal Recovery Strategies 220</p> <p>11.3 Other Considerations 228</p> <p><b>12 GEOREDUNDANCY REQUIREMENTS 230</b></p> <p>12.1 Internal Redundancy Requirements 230</p> <p>12.2 External Redundancy Requirements 233</p> <p>12.3 Manually Controlled Redundancy Requirements 235</p> <p>12.4 Automatic External Recovery Requirements 237</p> <p>12.5 Operational Requirements 242</p> <p><b>13 GEOREDUNDANCY TESTING 243</b></p> <p>13.1 Georedundancy Testing Strategy 243</p> <p>13.2 Test Cases for External Redundancy 246</p> <p>13.3 Verifying Georedundancy Requirements 247</p> <p>13.4 Summary 254</p> <p><b>14 SOLUTION GEOREDUNDANCY CASE STUDY 256</b></p> <p>14.1 The Hypothetical Solution 256</p> <p>14.2 Standalone Solution Analysis 259</p> <p>14.3 Georedundant Solution Analysis 263</p> <p>14.4 Availability of the Georedundant Solution 269</p> <p>14.5 Requirements of Hypothetical Solution 269</p> <p>14.6 Testing of Hypothetical Solution 277</p> <p><b>Summary 285</b></p> <p><b>Appendix: Markov Modeling of Service Availability 292</b></p> <p><b>Acronyms 296</b></p> <p><b>References 298</b></p> <p><b>About the Authors 300</b></p> <p><b>Index 302</b></p>

<b>Eric Bauer</b> is Reliability Engineering Manager in the IMS Solutions Organization of Alcatel-Lucent, where he focuses on reliability of Alcatel-Lucent's IMS solution and the network elements that comprise the IMS solution. He has written <i>Design for Reliability: Information and Computer-Based Systems</i> and <i>Practical System Reliability</i>. <p><b>Randee Adams</b> is a Consulting Member of Technical Staff in the Applications Group of Alcatel-Lucent. Currently, she is focusing on reliability for Alcatel-Lucent's software applications.</p> <p><b>Daniel Eustace</b> is a Distinguished Member of Technical Staff in the IMS Solutions Organization of Alcatel-Lucent. Currently, he is a solution architect focusing on reliability, key quality indicators, geographical redundancy, and call processing.</p>

<b>How Geographic Redundancy Can Improve Service Availability and Reliability of Computer-Based Systems</b> <p>Enterprises make significant investments in geographically redundant systems to mitigate the very unlikely risk of a natural or man-made disaster rendering their primary site inaccessible or destroying it completely. While geographic redundancy has obvious benefits for disaster recovery, it is far less obvious what benefit georedundancy offers for more common hardware, software, and human failures. <i>Beyond Redundancy</i> provides both a theoretical and practical treatment of the feasible and likely benefits from geographic redundancy for both service availability and service reliability.</p> <p>The book is organized into three sections:</p> <ul> <li> <p>Basics provides the necessary background on georedundancy and service availability</p> </li> <li> <p>Modeling and Analysis of Redundancy gives the technical and mathematical details of service availability modeling of georedundant configurations</p> </li> <li> <p>Recommendations offers specific recommendations on architecture, requirements, design, testing, and analysis of georedundant configurations</p> </li> </ul> <p>A complete georedundant case study is included to illustrate the recommendations. The book considers both georedundant systems and georedundant solutions. The text also provides a general discussion about the capital expense/operating expense tradeoff that frames system redundancy and georedundancy. These added features make <i>Beyond Redundancy</i> an invaluable resource for network/system planners, IS/IT personnel, system architects, system engineers, developers, testers, and disaster recovery/business continuity consultants and planners.</p>

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